Cell survival is regulated by various extracellular signals, for example, growth factors, cytokines, and extracellular matrices (ECM), via cell surface receptors.
Two major signal transduction pathways regulate the process of signal transduction from the cell surface to the nucleus. One is the Ras signaling pathway, and the other is the PI3K (Phosphatidylinositol 3 kinase) pathway. The PI3K pathway is either activated via cell surface receptors or indirectly by Ras. The present invention focuses on the Ras signaling pathway.
The MAPK (mitogen-activated protein kinase) cascade which comprises three kinases, namely, Raf, MEK (MAPK or ERK kinase), and ERK (extracellular stimulus regulated kinase), is a key component of the Ras signaling pathway. The cascade starts with the activation of Ras and in response to extracellular signals, plays an important role in regulating cell proliferation, differentiation, and transformation (Person, G., F. Robinson, T. Beers Gibson, B. Xu, M. Karandikar, K. Berman, and M. H. Cobb. Endocrine Rev., 22, 153-183 (2001); Bryan A. Ballif and John Blenis, Cell Growth & Differentiation, 12, 397-408 (2001); Cobb M H, Prog. Biophys. Mol. Biol., 71 479-500 (1999); Lewis T S, Shapiro P S and Ahn N G. Adv. Cancer Res., 74 49-139 (1998); Kolch W, Biochem. J., 351, 289-305 (2000); Judith S Sebolt-Leopold, Oncogene, 19, 6594-6599 (2000); Roman Herrera and Judith S. Sebolt-Leopold, Treds in Molecular Medicine, 8, S27-S31 (2002)).
Ras activation is regulated through the interplay between GTP-exchange factors (GEFs) and GTPase-activating proteins (GAPs) (Giorgio Scita, Pierluigi Tenca, Emanuela Frittoli Arianna Tocchetti, Metello Innocenti, Giuseppina Giardina and Pier Paolo Di Fiore, EMBO Journal. 19, 2393-2398 (2000)). GEFs activate Ras through the formation of Ras-GTP complex, and GAPs inactivate Ras through the formation of Ras-GDP complex. Ras activation results from growth factor-mediated extracellular signals to cell surface receptors or from Ras mutations. Ras mutations are found in many human cancer cells. It is known that such Ras mutations result in sustained Ras activation (GTP complex) and play key roles in the proliferation of human cancer cells.
Activated Ras interacts with Raf-1, a serine/threonine protein kinase, to activate Raf-1 (Daum G, Eisenmann-Tappe I, Fries H W, Troppmair J and Rapp U R, Trends Biochem. Sci., 19, 474-480 (1994); Stokoe D, Macdonald S G, Cadwallader K, Symons M and Hacock J F, Science, 264, 1463-1467 (1994)).
Activated Raf-1 then phosphorylates and activates MEK1 and MEK2. MEK is phosphorylated on two serine residues (Ser218 and Ser222) (Dent P, Haser W, Haystead T A, Vincent L A, Roberts T M and Sturgill T W, Science, 257, 1404-1407 (1992); Crews C M, Alessandrini A and Erikson R L, Science, 258, 478-480 (1992); Her J H, Lakhani S, Zu K, Vila J, Dent P, Sturgill T W and Weber M J, Biochem. J., 296, 25-31 (1993); Alessi, D. R., Y. Saito, D. G. Campgell, P. Cohen, G. Sithanandam, U. Rapp, A. Ashworth, C. J. Marshall, and S. Cowley. Trends Biochem. Sci. 21 373-372 (1994); Zheng, C. F., and K. L. Guan. J. Biol. Chem. 268, 23933-23939 (1993)).
MEK is a dual-specificity kinase. Activated MEK phosphorylates ERK1 and ERK2 on tyrosine (185) and threonine (183) residues (Anderson N G, Maller J L, Tonks N K and Sturgill T W, Nature, 343, 651-653 (1990); Seger R and Krebs E G, FASEG J, 9 716-735 (1995)).
The MEK-mediated ERK phosphorylation results in not only ERK activation but also translocation of ERK to the nucleus.
Activated ERK (MAPK) activates various substrates, for example, transcription factors in the cytoplasm and nucleus, and the result is that the activation leads to cellular changes (proliferation, differentiation, and transformation) depending on the extracellular signal.
MEK has a strict substrate specificity. ERK1 and ERK2 are the only substrates of MEK phosphorylation that have been identified (Seger R, Ahn N G, Posada J, Munar E S, Jensen A M, Cooper J A, Cobb M H and Kregs E G, J. Biol. Chem., 267, 14373-14381 (1992)).
Strict substrate specificity (limited substrates: ERK1 and 2) and dual specificity (phosphorylation on both tyrosine and threonine), which are unique properties of MEK bur rarely found in other kinases, are suggested to play a central role in the MEK integration of signals in the MAPK pathway.
Constitutive activation of the MEK/MAPK pathway is shown to be associated with the neoplastic phenotypes of a relatively large number of cancer cell types (Hoshino R, Chatani Y, Yamori T, Tsuruo T, Oka H, Yoshida O, Shimada Y, Ari-I S, Wada H, Fujimoto J, Kohno M, oncogene, 18, 813 (1999); Kim S C, Hahn J S, Min Y H, Yoo N C, Ko Y W, Lee W J, Blood, 93, 3893 (1999); Morgan M A, Dolp O, Reuter C W, Blood, 97, 1823 (2001)).
In addition, constitutive activation of MEK has been reported to result in cellular alteration (transformation or canceration) (Cowley S, Paterson H, Kemp P and Marshall C J, Cell, 77, 841-852 (1994); Mansour S J, Matten W T, Hermann A S, Candia J M, Rong S, Fukasawa K, Vande Woude G F and Ahn N G, Science, 265, 966-970 (1994)).
Furthermore, studies of MEK inhibitors (PD98059 and others) have revealed that MEK inhibition not only results in impaired cell proliferation, but also has impact on various cellular events, including cell differentiation, apoptosis, and angiogenesis (Dudley D T, Pang L, Decker S J, Bridges A J and Saltiel A R, Proc. Natl. Acad. Sci. USA, 92, 7686-7689 (1995); Alessi D R, Cuenda A, Cohen P, Dudley D T and Saltiel A R, J. Biol. Chem., 270, 27489-27494 (1995); Pages G, Lenorman D, L'Allemain G, Chambard J C, Meloche S and Puyssegur J, Proc. Natl. Acad. Sci. USA., 90, 8319-8323 (1993); Pang L, Sawada T, Decker S J and Saltiel A R., J. Biol. Chem., 270, 13585-13588 (1995); Finalay D, Healy V, Furlong F, O'Connell F C, Keon N K and Martin F, Cell Death Differ. 7, 303-313 (2000); Holmstrom T H, Tran S E, Johnson V L, Ahn N G, Chow S C and Eriksson J E, Mol. Cell. Biol., 19, 5991-6002 (1999); Elliceiri B P, Klemke R, Stromblad S and Cherexh D A, J. Cell Biol., 141, 1255-1263 (1998); Milanini J, Vinals F, Pouyssegur J and Pages G, J. Biol. Chem., 273, 18165-18172 (1998)).
The above-described findings suggest that MEK, one of the major mediators in the MAPK cascade, can serves as a potential target for therapeutic agents used in treating diseases caused by aberrant cell proliferation.
There are many previously reported MEK inhibitors including, for example, compounds having the backbone structure of a 2-phenylaminobenzoic acid or a derivative thereof, and which comprise various types of substituents at different positions (U.S. Pat. No. 6,251,943; U.S. Pat. No. 6,310,060; U.S. Pat. No. 6,506,798; International Publication WO 98/37881; WO 99/01421; WO 99/01426; WO 00/35435; WO 00/35436; WO 00/37141; WO 00/40235; WO 00/40237; WO 00/41505; WO 00/41994; WO 00/42002; WO 00/42003; WO 00/42022; WO 00/42029; WO 00/64856; WO 01/05390; WO 01/05391; WO 01/05392; WO 01/05393; WO 01/68619; WO 02/06213; WO 02/18319; WO 03/062189; WO 03/062191; WO 03/077855; WO 03/077914; WO 04/056789; and Japanese Patent Application Kokai Publication No. (JP-A) 2001-55376 (unexamined published Japanese patent application)). The previously reported compounds also include N-alkoxy-2-phenylamino-benzamide derivatives which have an alkoxy residue as the substituent on the amide nitrogen atom. Furthermore, the reported compounds also include compounds which comprise as a substituent, a halogen atom, a carbamoyl group, a sulfamoyl group, or such, at position 5 of the benzamide ring (International Publication WO 98/37881; WO 99/01426; WO 00/42003; WO 01/68619; and WO 02/06213).
Meanwhile, the anti-cancer effect of compounds comprising the feature of an MEK inhibitor, as reported, has been drawing attention. Such compounds include, for example, compound CI-1040 described below (in Example 95 of WO 99/01426). The result of a phase I clinical trial of compound CI-1040 was reported in the American Society of Clinical Oncology Annual Meeting in 2002 (American Society of Clinical Oncology Annual Meeting in 2002 (Abstract Nos. 320 and 321; May, 18-21, 2002)). However, various problems have been pointed out, for example, rapid hydrolysis and inactivation of the compound in vivo; high lipid solubility and low water solubility; and a wide interpatient variability in pharmacokinetic parameters. The clinical trial for CI-1040 was thus terminated. At present, PD0325901 (WO 02/06213) is currently at the stage of a phase II clinical trial in U.S.

Meanwhile, there are reports on methods of preventing or treating rheumatoid arthritis or osteoarthritis using compounds having MEK-inhibiting activity (International Publication WO 00/35436; WO 01/68619; and JP-A 2001-55376).